In recent years, various proposals for further improvement of the light utilization efficiency and the energy saving in optical elements such as displays, light-emitting diodes, and solar cells have been done. For example, it has been known in a liquid crystal display to raise an aperture ratio of the display device by forming a transparent planarization film by application on a TFT element and then forming a pixel electrode on the planarization film (see the patent document 1 below). Further, in an organic EL device, it has been known to raise an aperture ratio thereof like a liquid crystal display by adoption of a top emission which is a method taking out emitted light by a luminous layer, which is formed on a transparent pixel electrode existing on a planarization layer formed on a TFT element by application, from the opposite side of a TFT element instead of a bottom emission which is a method taking out emitted light by a luminous layer, which is formed by a deposition on a transparent pixel electrode formed on a substrate, from the side of the substrate.
Furthermore, delay in signal on wiring becomes a problem accompanying to increasing in resolution, size, and picture quality as well as 3D indication of a display. An incoming signal to a TFT becomes shorter by increasing of writing speed of an image data (frame frequency) but there is a limit on linewidth extension of wiring for lowering a wiring resistance from a demand of high resolution. Because of this, it is proposed to solve the problem of signal delay by increasing the thickness of wiring (see the non-patent document 1 below).
As materials of the planarization film for the TFT substrate, there has been known a material in which an acrylic resin and a quinonediazide compound are combined (see patent documents 3 and 4 below). Though properties of the material do not deteriorate sharply at a high temperature of 200° C. or more, decomposition thereof begins gradually at a high temperature of 230° C. or more and there occur problems such as lowering of a film thickness and lowering of permeability due to coloring of a transparent layer by a high temperature processing of the substrate. Particularly, this material cannot be used in a process for forming a film on a layer of the material at a high temperature by use of devices such as a PE-CVD. Further, the material is not a best material for use in an organic EL element, as decomposition products thereof affect badly to the luminous efficiency and the life of an organic EL element. Furthermore, the acrylic material to which a heat resistance is given has a high dielectric constant generally. The material, therefore, has problems that electricity consumption becomes larger due to the increase in the parasitic capacitance of an insulation film and the picture quality decreases due to the delay in a driving signal of a liquid crystal element. The capacitance of the film can be made smaller by, for example, making a thickness of a film layer larger even if the film forming material is an insulate material with a large dielectric constant. However, formation of a thick film with a uniform film thickness is generally difficult. In addition, the amount of the material used becomes larger. The material, therefore, is not preferred.
Polysiloxanes, in particular, silsesquioxanes are known as materials with a high thermal resistance and a high transparency. Silsesquioxanes are polymers constructed by a three-functional siloxane structure unit: RSi(O1.5) and are in between an inorganic silica (SiO2) and an organic silicone (R2SiO) with respect to the chemical structure. The polysiloxanes are singular compounds as it is, which are soluble in an organic solvent but a cured polysiloxane shows a high thermal resistance which is characteristic of inorganic silica. The polysiloxanes which are a component of a photosensitive composition need to dissolve in developers such as a tetramethylammonium hydroxide aqueous solution. There were proposed, therefore, a photosensitive composition comprising an acrylic copolymer copolymelized with a silsesquioxane compound in which an acrylic group is given to a particular caged silsesquioxane compound, an unsaturated carboxylic acid, an unsaturated compound containing an epoxy group, and an olefinic unsaturated compound, and a quinonediazide (see patent document 5 below). The compositions comprising complicated systems described above, however, give a cured material with an insufficient thermal resistance due to the thermal deterioration of organic compounds except for the polysiloxanes, as the amount of the organic compounds contained is large. The problems of coloration and gas generation due to the decomposition cannot be ignored.
As a photosensitive composition comprising a polysiloxane and a quinonediazide, there was proposed a photosensitive composition preventing a ‘pattern’ sagging, that is, hole or line patterns obtained after development flowing and as a result the resolution of the patterns becoming low at a heat curing, for example, by combining a system consisting of a polysiloxane which is insoluble in a developer and a polysiloxane which is soluble in a developer, and a quinonediazide compound (see patent document 6 below). If an insoluble polysiloxane in a developer is used, it will cause generating pattern lacks due to re-adhesion of slightly soluble materials or eluted insoluble materials during development.
As methods for retaining solubility in developer except a silanol group, there were proposed methods acylating a part of phenyl groups in phenylpolysiloxane (see patent document 7 below) and using a caged silsesquioxane compound having quinonediazide structure (see patent document 8 below). As these siloxanes have a stable developer-soluble group even if silanol groups react during development, problems of forming an insoluble layer and undissolved remains are reduced. The cured materials of these polysiloxanes, however, have poor resistance for chemicals such as a stripper for photoresist. These compounds have limit uses enabled.